Silicate Phosphor Thermal Stability and White Light Continuity
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Solution Overview
Problem
Conventional white light emitting diodes (wLEDs) using yellow phosphors suffer from insufficient green and red intensity, temperature-dependent emission luminance and color variation, and complex, costly manufacturing processes.
Innovation Solution
A silicate phosphor with a γ-phase orthorhombic crystal structure, represented by Chemical Formula Ca2-x-y-zMxSiO4:yCe3+,zQ, where M and Q include various metals and activators, is developed, allowing for high green and red emission efficiency, stability at elevated temperatures, and simplified manufacturing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If YAG-based phosphor is used to generate yellow light, then the white light can be formed by mixing blue light and yellow light, but the green intensity and red intensity in the emission spectrum are insufficient resulting in low continuity of the white light
Solution Approach 1:
The patent uses a composite phosphor system combining Y3Al5O12:Ce3+ (yellow phosphor) with (Ba,Sr,Ca)2SiO4:Eu2+ (green phosphor) to create a multi-component material that emits both yellow and green light, thereby improving the continuity and quality of the resulting white light while maintaining the simplicity of the LED structure
2Illumination intensity
If BOS-based phosphor is used to generate yellow light, then the white light can be formed, but the emission luminance is reduced and emission color is changed at elevated temperatures causing temperature-varied performance
Solution Approach 1:
The patent selects specific phosphor materials with appropriate activation energies for their emission transitions. The Y3Al5O12:Ce3+ phosphor has high thermal stability while the (Ba,Sr,Ca)2SiO4:Eu2+ phosphor is chosen for its temperature-resistant properties, creating a system where each component contributes its optimal thermal characteristics to the overall white light output
3Ease of manufacture
If nitride/nitric-based phosphor manufacturing process is used, then the phosphor can be produced, but the process requires high temperature and high pressure resulting in expensive devices and low yield ratio due to difficult size control, separation and grinding
Solution Approach 1:
The patent adopts a solid-state reaction method that operates at moderate temperatures (900-1100°C) and atmospheric pressure, fundamentally changing the manufacturing parameters from the conventional high-temperature high-pressure nitride process. This parameter change enables simple mixing of raw materials, straightforward sintering, and easy particle size control through conventional grinding, dramatically improving both ease of manufacture and productivity
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The silicate phosphor achieves high emission efficiency and stability at high temperatures, maintaining over 60% luminance above 200°C, with minimal color variation, and enables the production of various white light types from warm to cold white light.
Implementation Method 1
a silicate phosphor having a γ-phase of an orthorhombic crystal structure whose space group is Pbnm 62, and whose composition is represented by the following Chemical Formula 1: Ca2-x-y-zMxSiO4:yCe3+,zQ (0≦x<0.5, 0<y<0.1, 0≦z<0.15)
Implementation Method 2
the silicate phosphor composition maintains a stable emission luminance at high temperatures, and has a relatively small color variation in response to temperature change
Data Source
AI summary
A silicate phosphor composition is provided having a γ-phase of an orthorhombic crystal structure whose space group is Pbnm 62, and whose composition is represented by the following chemical formula: Ca2-x-y-zMxSiO4:yCe3+,zN(0≦̸x<0.5,0<y≦̸0.1,0≦̸z<0.15) In the formula, M represents at least one member selected from the group consisting of Mg, Sr, Ba, Zn, Na, Al, Ga, Ge, P, As and Fe, and N represents at least one member selected from the group consisting of Eu2+, Mn2+, Tb3+, Yb2+ and Tm3+. The silicate phosphor has a maximum absorbance for a wavelength of about 450 nm to about 475 nm corresponding to a main part of a blue excitation light, and has a great stability at a high temperature. As such the silicate phosphor may be used in combination with a blue light source to produce a white light.